AWWA WQTC62395

Endotoxins are a component of the lipopolysaccharide complexes that make up a part of the outer layer of the cell walls of most gram-negative bacteria and some cyanobacteria. Laboratory filter column tests to identify conditions under which endotoxins can be released from biologically active drinking water treatment anthracite/sand filters showed that endotoxin was produced in large quantities in the first few hours following shutdown. However, accumulated endotoxin can be easily dealt with by immediately backwashing or running filters to waste following periods of shutdown. Free chlorine, monochloramine, and potassium permanganate were not particularly efficient at inactivating endotoxin, with the maximum inactivation rate being 1.4 endotoxin units (EU)/mL.h for free chlorine. Medium pressure ultraviolet irradiation was somewhat effective (~0.55 EU/mL per mJ/cm²), although higher dosages than those currently being employed in drinking water treatment would be required to effectively remove higher concentrations. Using a range of drinking water endotoxin concentrations measured in biofilter shutdown experiments and from values recorded in the literature, endotoxin aerosolization associated with humidifiers was examined. A theoretical assessment suggests that ultrasonic humidifiers are able to produce quantities of aerosolized respirable endotoxin sufficient to easily induce adverse health impacts, including those requiring medical attention. In addition to being a health hazard on its own, endotoxin may exacerbate existing medical conditions and may confuse physicians attempting to diagnosis multiple symptoms. Includes 22 references, table, figures.